Chrome on Android has an ever growing list of requirements for UI at the bottom of the screen. We should build a more generic "infobar" system that supports the following:

- Persistent infobars across tabs ("app-level").
- Formal prioritization; when other infobars claim to be more important than ones already showing.
- More freedom for feature teams to customize.

On the technical side, we have the following goals:
- Build an easily extensible system.
- Remove dependence on native; at least for creating a new infobar. Currently there is tremendous overhead in creating a new infobar.
- Build a system that allows new infobars and old to exist simultaneously (as some don't have a conversion path).

This bug serves as tracking for the work associated with this task.